The Regulation Of CAMP-PKA Pathway And Its Role In Ocular Dominance Plasticity

Study on the molecular mechanism of neural development plasticity has been a hot spot in research of brain science.As a classic model of brain plasticity research,visual cortex has been studied for many years and its functional architecture is also clear.Ocular dominance plasticity(ODP)is defined as the reduced response to the deprived eye and the enhanced response to the non-deprived eye after monocular deprivation(MD)during the critical period.As a second messenger pathway,it has been reported that cyclic AMP-protein kinase A(cAMP-PKA)pathway is crucial to visual plasticity.However,it is still unclear about the upstream and downstream of cAMP-PKA pathway in ODP.In this study,we investigated two molecules,phosphodiesterase 4D(PDE4D)and A-kinase anchoring proteins(AKAPs),which may control ODP though the regulation of cAMP-PKA pathway.Previous studies have demonstrated that cAMP is curial for expressing visual plasticity during the critical period.The PDE4 enzyme family has been proved to be important to synaptic plasticity through specific hydrolysis of cAMP.However,the role of PDE4 in ODP is unknown.Here,we investigated the involvement of PDE4D,one isoform of PDE4,in regulating visual plasticity during development in mice and kittens.In mice,the level of PDE4D in V1 was assaied through western blot at different time points.We found that the expression in the visual cortex of PDE4D matched the process of ODP.PDE4D showed a lower level in the early development,while peaking in the critical period,and then declined after the critical period.However,changing the visual experience,such as dark rearing(dark rearing,DR)or MD did not affected the PDE4D level in visual cortex,suggesting that PDE4D expression is not dependent on the visual experience.Using optical imaging found that mice whose OD shift induced by visual deprivation was not impaired after the injection of rolipram,a selective inhibitor of PDE4,during the critical period.Meanwhile,in kittens(1 month and 2 months),the OD shift was also not impaired after the administration of rolipram or Dimethyl Sulphoxide(DMSO)into the primary visual cortex with osmotic minipump two days prior to the one day or four days MD.Together,these findings implied that PDE4D was development-dependent and may not correlate with the plasticity induced by visual experience.Secondly,PKA anchoring to AKAPs is required for ODP.Previous studies demonstrated that ODP is regulated by the PKA signaling pathway.Infusion of PKA inhibitor into primary visual cortex or knockout of PKA RII subunits impaired the OD shift induced by MD during the critical period.PKA has hundreds of protein targets.Accumulated evidences suggest that PKA anchoring to AKAPs is important for the kinase to exert its specific function in different compartments of the cell.In this study,we examed the ODP in AKAP150 knockout mice.The degrees of the OD shift of AKAP150-/-mice were less than the MD group after four days MD.To excluding the side effects of knockout,we investigated the role of PKA compartmentalization in ODP with St-Ht31,which is a membrane permeable peptide and disrupts the binding of PKA and AKAPs,and its control peptide St-H31P in mice and kittens.Animals were infused St-Ht31/St-H31P to the left hemisphere of V1 area.After four days MD of the right eye,using single unit recordings we found that the St-Ht31 impaired the OD shift comparing with St-Ht31P and control group,but no significant changes in functional properties of visual cortical neurons in the recorded animals.It suggested that blocking PKA anchoring to AKAPs resulted in an inhibition of ODP in mice.In contrast,the OD shift of St-Ht31 group was similar with St-Ht31P after four days MD in kittens indicating the St-Ht31 did not affect the ODP in kittens.These results suggest that the spatial compartmentalization of PKA signaling pathways,achieved by anchoring of PKA to AKAPs,is required for ODP in mice but not kittens.